Generally, hard-disk drives have rotating high precision disks that are coated on both sides with a special thin film media designed to store information in the form of magnetic patterns. In bit-patterned, hard-disk drives, the special thin film media has been patterned to form a large number of individual storage elements that can retain a magnetic orientation and thereby store data. Electromagnetic read/write heads “flying” on a cushion of air only fractions of micro-inches above the disk are used to record information onto the thin film media or read information from the media. Read/write heads may write information to the disk by creating an electromagnetic field to orient magnetic grains of a storage element in one direction or the other. Each grain acts as a magnetic dipole pointing in a certain direction and creating a magnetic field around the grain. All of the grains in a storage element will typically point in the same direction so that the storage element as a whole has an associated magnetic field. Read/write heads may read information from the disk by sensing the direction of a magnetic field associated with the storage elements.
Because read/write heads are used to sense and orient the magnetic fields of a storage element, proximity of the read/write heads can be quite important. For example, when the read/write heads are located closer to a storage element, it may be possible to more accurately and efficiently write to or read from the storage element, which can lead to better hard-disk drive performance in the form of speed and efficiency. Further, increased proximity between read/write heads and storage elements can even lead to better data retention and a reduced likelihood of data corruption because the magnitude of the static magnetic fields necessary for reading and the magnitude of the induced magnetic fields for writing may be reduced. The reduced magnitudes may lead to less detrimental interaction between a storage element and a magnetic field induced by the read/write head and/or nearby storage elements.
While it may be desirable to have the read/write head as close to the storage elements as possible, it may also be undesirable that the read/write head contact the thin film medium. For example, contact between the read/write head and the thin film medium can damage the storage elements and cause the contacted portion to become inoperable. Thus, it is important to balance proximity of the read/write head with the risk of the read/write head contacting the thin film medium.
Two major aspects of the design of thin film media can lead to increased proximity between a read/write head and the storage elements. A first aspect is the thickness of the intervening layers between a surface of the thin film medium and the magnetic region of a magnetic storage element. Reduced overall thickness of these intervening layers can allow a read/write head to be closer to the magnetic region. A second aspect is the planarity of the surface of the thin film medium. Generally, the more planar or smooth the thin film medium is, the closer the read/write head can be to the storage elements because the lower the risk of the head contacting the surface of the medium. Because the patterning of a thin film can, in some embodiments, lead to bumps or other surface features on the thin film, this can be an important consideration.
Additionally, manufacturing of patterned features on the thin film can be quite complicated and involve multiple steps which may include forming multiple layers, etching one or more layers, planarizing, or other steps. Each step adds to the complexity which increases cost, risk of failure, and/or other problems. Thus, reducing the number of layers or fabrication steps may reduce the cost of fabricating a storage medium. This reduction of layers and manufacturing complexity must be balanced with the desired quality and density of magnetic storage.